A world away from Sherlock Holmes, Benedict Cumberbatch's latest television
role sees him playing a repressed civil servant

Benedict Cumberbatch has fallen in love with an overweight civil servant called Christopher. 'I am enamoured of his principles, his virtue and the goodness he stands for,' he says, grinning the wonky grin of the hopelessly smitten. 'I love him. I really do think that Christopher Tietjens is the character I'm most fond of ever having played.'

Tietjens needs all the love he can get. The anti-hero of Parade's End – a tetralogy of novels written by Ford Madox Ford in the 1920s, about the life and relationships of Tietjens before and during the First World War, and now adapted by Tom Stoppard into a five-part television drama – may be intellectually sharp, but he's physically cumbersome and all but incapable of articulating the emotion buried beneath his ungainly exterior. 'As Tietjens saw the world, you didn't "talk",' Ford writes. 'Perhaps you didn't even think about how you felt.'

Cumberbatch's performance, in an ambitious series co-produced by the BBC with the American network HBO, is mesmerising; it is further proof of his knack for making even the most peculiar characters seem overwhelmingly human. While his Sherlock Holmes, the character that made him a household name and bona fide heart-throb, may share a certain cruel wit with his Tietjens, in other ways the two figures could hardly be more different. If Sherlock zips breakneck across the screen like a jet ski, Tietjens glides, with the stately movement of an ocean liner. Where Sherlock arrives at the truth by employing what Cumberbatch calls his 'sociopathic, motormouth deducting genius', Tietjens seems to carry it within him.

His Tietjens is the kind of man who will pore over the Encyclopaedia Britannica, scribbling corrections in the margin, while the nation stands on the brink of war, and his wife (Rebecca Hall) – a volatile beauty who is openly cheating on him with another man – hurls insults at him across the breakfast table. 'He tries to kill her with kindness,' Cumberbatch says. 'But what she really wants from him is to be told to stop f***ing around, not be mollycoddled and treated as damaged goods.'

The make-up department helped with the actor's physical transformation, dyeing his naturally ginger hair blond, padding out his tall, slender body, and stuffing his long, hollow cheeks with plastic plumpers. 'I had Boris Johnson as a visual reference,' Cumberbatch says, retracting his angular face into his neck and tugging at his jowls. 'I wanted to go further with it… but I think they were slightly nervous about any kind of attractiveness being completely lost.'

It is a dull July afternoon and we are talking over lunch in an airy restaurant in west London. Cumberbatch speaks in sentences of extravagant length and confidence. 'The tragedy is that Tietjens and his wife love each other, it's just the wrong kind of love, expressed in the wrong kind of way,' he says. 'There but for the grace of God a lot of us might go, or are going, or have gone.'

The role of the cerebral maverick is not untrodden ground for Cumberbatch. He came to prominence playing Professor Stephen Hawking for a one-off BBC drama in 2004, and last year starred as both Victor Frankenstein and his monster at the National Theatre, alternating the roles with his co-star Jonny Lee Miller. Nor is he a stranger to playing the upper-class British male. Indeed, having portrayed so many – his plummy creations in Starter for 10, Atonement, Tinker Tailor Soldier Spy and War Horse most memorable among them – he says he had sworn off privileged characters, fearful of type-casting, until Tietjens came along, and his resistance collapsed.

Cumberbatch still recalls the moment in 2010 when Stoppard arrived unannounced on the West Country set of War Horse, Steven Spielberg's First World War epic in which he played the cavalry officer Major Stewart. 'We were between takes on the battlefield, it was raining heavily, and Tom just kept saying to me, "You're having such a remarkable year, Benedict, such a remarkable year." Then he would suck on his Silk Cut and stare at the ground. It was very odd. I subsequently found out he couldn't bring himself to look at me properly because I was in First World War clobber, and although I was thin and moustachioed and ginger for that part, he saw in me then the image of Christopher Tietjens. Apparently, he'd been thinking about me playing that role for years, and had even mentioned me when it was first talked about as a project, pre-Sherlock, when the backers in America were going, "Benedict who?".' A flicker of satisfaction passes across his face.

'I felt wretched,' Stoppard says later, when I relate to him Cumberbatch's account of their encounter on the battlefield. 'It was like meeting our Christopher. But there were a few bumps in the road still to come.'

In January last year those bumps had been broached and Stoppard, together with Susanna White, the director of Parade's End (and before that, of Bleak House), was finally in a position to offer the role formally to Cumberbatch. By then the BBC's full-throttle Sherlock Holmes reboot had made him a star on both sides of the Atlantic, Frankenstein had sold out its entire run at the National, and HBO had gone from questioning his involvement in Parade's End to more or less insisting upon it. 'It was a mark of how crazy and different things have got,' Cumberbatch says, his pale eyes glinting.

At the age of 36, having spent more than a decade laying down the foundations of a successful stage, radio and screen career, predominantly in what he identifies as the kind of 'quite strange, esoteric, non-commercial ventures' that earn an actor respect among his peers but little in the way of celebrity, Cumberbatch is on his way to becoming a major player in the film industry. When we meet he has just returned from six months abroad, filming parts in both The Hobbit and J J Abrams's Star Trek sequel – two films the sheer scale of which exceed anything he has been involved in before. By the time you read this article, he will be in New Orleans, starring as a 19th-century slave owner alongside Brad Pitt and Michael Fassbender in Steve McQueen's new film, Twelve Years a Slave. As Cumberbatch puts it, 'It's all gone a little bit vertiginous recently.

'Fame is a weird one,' he adds. 'You need to distance yourself from it. People see a value in you that you don't see yourself. So when I'm told of my sex-symbol status and all that nonsense I find it laughable, silly. I mean, look.' He gestures towards his face. 'I'm 36 and I've been looking at this same old mush all my life.'

Born in London to the actors Timothy Carlton and Wanda Ventham (who also has a daughter from a previous relationship), Cumberbatch says that his own desire to act 'was sort of there always. I mean I toyed with the idea very seriously of being a barrister for a while, but I think that was more to show off to my parents that I was capable of that.' He acted throughout his school days, beginning at a pre-prep school in Notting Hill where he starred as Joseph in the nativity play and earned his first, intoxicating laugh from the crowd when he shoved the girl playing Mary off the stage. 'I didn't really understand it, and I wasn't intending to play to the house,' he says. 'I was just furious about how self-indulgent she was being.' From there he went on to a boarding school in Sussex, where the teachers urged him on to the stage, partly as a form of behaviour management. 'I think it was almost like a control thing, to repress the tearaway in me,' he says. 'I was pretty naughty, I got into fights, it was all a bit Just William.

'Then I went to Harrow, and that was really the moulding of me. In my first year I had the onerous task, having just established myself as a reasonably decent rugby-playing cricketer and footballer, of starring as Titania, Queen of the Fairies. I then followed up with a Rosalind that was deemed by my drama tutor as being the finest since Vanessa Redgrave's.' He laughs. 'I have seen pictures of that and it's quite scary – I look like I am possessed by a woman.'

It was while he was performing in a school production that Cumberbatch first met Rebecca Hall, his friend and co-star in Parade's End and, before that, Starter for 10. She was eight years old and he was in the same class as the older brother of her best friend, with whom she went to see the performance. 'Benedict was one of those boys that you met and you could already see what he was going to be like when he was middle-aged,' she tells me later, when we speak by telephone. 'He is a one-off, and it is the fate of people who are unique for others not to notice their talent straight off the bat. It's easy for people to say, "Wow, you are the next Johnny Depp." Benedict was never going to be the next anybody. He was always going to be just who he is.'

Towards the end of Cumberbatch's time at Harrow the film director Andrew Birkin held a casting at the school for his film of the Ian McEwan novel The Cement Garden, about incest between teenage siblings. Cumberbatch was invited to audition. 'I was really prudish at that age and thought, "F*** it, I don't want to take my clothes off." I was terrified, I didn't want anyone seeing what I looked like,' he says. 'So I didn't audition, but I think that was the moment when I stumbled into realising that acting could be a thing for life rather than just something I did during term time.'

From Harrow he went to the University of Manchester to study drama, a deliberate detour from the Oxbridge route taken by so many of his peers. 'Not that Manchester was really roughing it,' he says, 'but I didn't want just an extension of my public school when I went to university. I wanted less exclusivity. I wanted more of life.'

After Manchester he returned to London, trained for a year at Lamda and started landing his first professional roles soon after, his reputation growing incrementally ever since. 'You can't predict how it's going to turn out,' he says. 'I think what happens is you do your bit, you settle, and see sort of where you are in the grand picture of where everyone else is, and you go, "Ooh, I'd like a bit of what that person's doing, and I think I can get up to that standard, and I think I could be taken seriously enough to do that." ' Did he ever doubt he would be able to sustain an acting career, I ask. 'It sounds really arrogant but I don't think I did, no,' he says. 'I'm not someone who's naturally confident, I just knew no matter what it held for me, I was going to pursue it.' There are still moments, he says, when his confidence falters. The first day he stepped on set of the new Star Trek film, joining an illustrious line of British stars who have played the villain in a Hollywood blockbuster, he had a momentary feeling of being out of his depth. 'I didn't know what I was going to do and I had very little time to establish the character in that franchise,' he says.

Filming The Hobbit brought challenges of a different kind. Although he plays two roles, a necromancer and Smaug (a fantastical villain he describes with undisguised glee as 'a 400-year-old fire-breathing worm who lives in the middle of a mountain on top of a pile of gold, who is three or four times bigger than the Empire State Building and can fly'), he barely encountered any other members of the cast. He worked on his scenes with the director, Peter Jackson, shooting against a green screen while wearing a motion-capture suit. 'It's sort of a grey all-in-one jumpsuit, with a skullcap, a Madonna headset and Aboriginal-like face paint,' he explains. 'You feel like a tit in all that gear but Peter is so lovely you soon forget.'

His ambitions are far from fulfilled. He has a hunger to direct, 'to be able to see a project from inception to fruition. As an actor you are never there for every heartbeat of it.' He also longs for a family of his own. 'I've been broody since I was 12, but I can't just get anyone pregnant, it has got to be the right person,' he says. I can't imagine he has much time to look these days. 'To find the right person? Oh well, there's always a way isn't there –and I don't mean the internet,' he adds, laughing. 'I mean there are always moments and meetings and chance encounters. But to make meaningful relationships is very hard at the moment. Also, I was in a very, very long relationship all through my twenties and early thirties [to The Thick of It actress Olivia Poulet], so I know about looking for the right one, I guess. And it's tough, it's tough.' For the time being, he says, he is single.

I ask if he feels guilty about the material trappings that success in show business brings. 'Of course I do,' he says. 'I've done very well in a very bad time for our profession, which is weird. When you start getting jobs, and see your mates from drama school, you don't really want to talk about it, because you have this innate sense of guilt that it's not fair that others aren't doing exactly what you're doing. I do have that. The number of people my age, younger now, a whole generation younger, who are fiercely bright, over-educated, under-employed and who are politicised and purposeless really upsets me. It's soul-destroying. So there is a kind of weird guilt about doing well.

'It's interesting, but only very recently have I found myself able to say, "I've got some money in the bank account. I am allowed to enjoy this." But at the beginning, and even now, actually, to be really honest, I'm simply thrilled to be getting money to act. Although,' he adds, looking worried, 'I don't know if you should be putting that in print. If any producers read it, they'll stiff me on my next fee.'